Li Cui

Confined Discotic Liquid Crystalline Self-Assembly in a Novel Coil−Coil−Disk Triblock Oligomer

An asymmetric ABC coil-coil-disk triblock oligomer, based on polyethylene-block-poly(ethylene oxide)-block-pentakis(pentyloxy)triphenylene (PE-b-PEO-b-P5T or EEO-P5T), was successfully synthesized by coupling a hydroxyl-terminated PE-b-PEO diblock oligomer and 2-hydroxy-3,6,7,10,11-pentakis(pentyloxy)triphenylene using oxalyl chloride. The structure and morphology of the supra-molecular self-assembly in bulk EEO-P5T were studied by differential scanning calorimetry, small- and wide-angle X-ray scatterings, polarized light microscopy, and transmission electron microscopy. The PE block crystallized into interdigitated, extended chain crystals with a chain-tilting angle of 23° from the lamellar normal. The peak melting temperature (T m ) of the PE crystals was at 93.8 °C. The PEO block remained in the amorphous state because of its both ends being tethered to other two blocks and the mismatch of the cross-section areas at the PE-PEO and PEO-P5T interfaces. Bilayer P5Ts, sandwiched between amorphous PEO layers, exhibited a nematic columnar (N col ) to nematic discotic (N D ) transition at ca. 23 °C. Intriguingly, the N D to isotropic (or vice versa) transition was observed to coincide with the melting (or crystallization) of the PE block.

Epitaxial Phase Transformation between Cylindrical and Double Gyroid Mesophases

Complex phase transformation between the hexagonal cylinder (Hex) and double gyroid (G) phases in a polystyrene-block-poly(ethylene oxide) (PS-b-PEO) diblock copolymer was investigated using two-dimensional (2D) synchrotron small-angle X-ray scattering (SAXS), and transmission electron microscope (TEM). The PS-b-PEO sample contained a small population of another bicontinuous cubic phase having an m Im3 symmetry. These two bicontinuous cubic phases (G and m Im3 ) had the same unit cell dimensions. Under a large-amplitude reciprocating shear, the bicontinuous cubic phases transformed into a “single-crystal”-like Hex phase. When annealed at 150 °C for 40 min, the Hex phase partially transformed into well-oriented twinned structures of the G and m Im3 phases without significant loss of orientation in 2D SAXS measurements. Epitaxial phase transformation relationships between the Hex/G and Hex/ m Im3 phases were identified. The mechanism of the Hex → G transformation was examined by TEM.

CONFINED DISCOTIC LIQUID CRYSTALLINE SELF-ASSEMBLY IN A NOVEL COIL-COIL-DISK TRIBLOCK OLIGOMER

An asymmetric ABC coil-coil-disk triblock oligomer, based on polyethylene-block-poly(ethylene oxide)-block-pentakis(pentyloxy)triphenylene (PE-b-PEO-b-P5T or EEO-P5T), was successfully synthesized by coupling a hydroxyl-terminated PE-b-PEO diblock oligomer and 2-hydroxy-3,6,7,10,11-pentakis(pentyloxy)triphenylene using oxalyl chloride. The structure and morphology of the supra-molecular self-assembly in bulk EEO-P5T were studied by differential scanning calorimetry, small- and wide-angle X-ray scatterings, polarized light microscopy, and transmission electron microscopy. The PE block crystallized into interdigitated, extended chain crystals with a chain-tilting angle of 23° from the lamellar normal. The peak melting temperature (T m ) of the PE crystals was at 93.8 °C. The PEO block remained in the amorphous state because of its both ends being tethered to other two blocks and the mismatch of the cross-section areas at the PE-PEO and PEO-P5T interfaces. Bilayer P5Ts, sandwiched between amorphous PEO layers, exhibited a nematic columnar (N col ) to nematic discotic (N D ) transition at ca. 23 °C. Intriguingly, the N D to isotropic (or vice versa) transition was observed to coincide with the melting (or crystallization) of the PE block.

Confined Discotic Liquid Crystalline Self-Assembly in a Novel Coil-Coil-Disk Triblock Oligomer

An asymmetric ABC coil-coil-disk triblock oligomer, based on polyethylene-block-poly(ethylene oxide)-block-pentakis(pentyloxy)triphenylene (PE-b-PEO-b-P5T or EEO-P5T), was successfully synthesized by coupling a hydroxyl-terminated PE-b-PEO diblock oligomer and 2-hydroxy-3,6,7,10,11-pentakis(pentyloxy)triphenylene using oxalyl chloride. The structure and morphology of the supra-molecular self-assembly in bulk EEO-P5T were studied by differential scanning calorimetry, small- and wide-angle X-ray scatterings, polarized light microscopy, and transmission electron microscopy. The PE block crystallized into interdigitated, extended chain crystals with a chain-tilting angle of 23° from the lamellar normal. The peak melting temperature (T m ) of the PE crystals was at 93.8 °C. The PEO block remained in the amorphous state because of its both ends being tethered to other two blocks and the mismatch of the cross-section areas at the PE-PEO and PEO-P5T interfaces. Bilayer P5Ts, sandwiched between amorphous PEO layers, exhibited a nematic columnar (N col ) to nematic discotic (N D ) transition at ca. 23 °C. Intriguingly, the N D to isotropic (or vice versa) transition was observed to coincide with the melting (or crystallization) of the PE block.